The ICJ Advisory Opinion on nuclear weapons and international humanitarian law

The ICJ Advisory Opinion on the lawfulness of nuclear weapons was given 20 years ago, and there has been very different opinions as to whether it clarified or confused the question of how nuclear weapons are regulated by international law, and particularly international humanitarian law. Both from a legal and a political perspective, the Opinion has played and continues to play a key part in the discussions on nuclear disarmament.

I will address an aspect of the Advisory Opinion that did confuse rather than clarify how IHL applies to nuclear weapons. This relates to the blurring of the lines between the law that regulates when is it lawful to resort to the use or threat of armed force (jus ad bellum) and the law on what means and methods can be used in war – regardless of the war’s justification (jus in bello – or IHL). It is important to keep these two legal regimes separate. One cannot, for example, attack enemy civilians because the enemy unlawfully started the war.

The question that was posed to the ICJ by the General Assembly was:

‘Is the threat or use of nuclear weapons in any circumstance permitted under international law?’

In its response, the ICJ did not distinguish clearly between the two concepts of threats or use, and it did not separate clearly the two legal regimes (jus ad bellum and jus in bello).

To start with the latter of these two elements: The Court stated that it could not conclude definitely on the lawfulness of the use of nuclear weapons ‘in an extreme circumstance of self-defence, in which the very survival of a State would be at stake.’

Did the Court by this mean that IHL obligations, in such circumstances, could be set aside?

Some commentators have suggested that the this wording in the Advisory Opinion must be interpreted to mean that one cannot exclude that the use of nuclear weapons would be lawful in such extreme circumstances, but only when the conditions of IHL are satisfied.

Other commentators have argued against this view; mainly because the preceding paragraph in the Advisory Opinion states that the threat or use of nuclear weapons would generally be contrary to the rules of IHL. The inference seems to be that IHL does not always (only generally) apply.

Only a situation of armed conflict triggers IHL, and many situations of armed conflict could arguably be seen as ‘extreme circumstances of self defence’. If this kind of legal justification for the use of force determines whether or not nuclear weapons can be used, then by implication, IHL will effectively be set aside.

The second element of the Advisory Opinion that contributed to mixing IHL and the rules of the UN Charter is that the Court referred to threats in the same manner as use:

The Court stated several times that the threat of use of nuclear weapons would be a violation of not only the Charter, but also of international humanitarian law. The term ‘threat or use of force’ is thus used throughout the Advisory Opinion as if it were also part of IHL. The Court even stated specifically that if the use of nuclear weapons would be prohibited under IHL, then the threat of use of nuclear weapons would also be prohibited under the same rules.

But IHL, by and large, does not regulate threats. In spite of this, the Court explicitly stated that: ‘If an envisaged use of weapons would not meet the requirements of humanitarian law, a threat to engage in such use would also be contrary to that law.’ The Court did not, however, explain how it came to this conclusion.

There are two specific provisions that pertain to threats under the general rules of IHL, laid down in AP I (and AP II) to the Geneva Conventions.

The first is the rule on quarter – (Article 40 in AP I), which states that: ‘It is prohibited to order that there shall be no survivors, to threaten an adversary therewith, or to conduct hostilities on this basis.’

Thus, in addition to the prohibition against ordering that there will be no survivors, there is also a prohibition against making such threats. The reason is the escalation of hostilities that would follow if one party fears that surrender or capitulation equals certain death. There must be a right to surrender or to take prisoners during or at the end of hostilities. This is secured through Article 40.

During the proceedings on the Advisory Opinion, the Solomon Islands argued that threats of use of nuclear weapons would be a violation of this rule, and said that: ‘Given the inevitability of the lethal effects of nuclear weapons, threatening their use must surely also violate the rights of potential victims as set forth in Article 40 of the 1st Additional Protocol…’

Hence, the question is whether the threat to use nuclear weapons would constitute a violation of Article 40 as such. In other words, could it be argued that any use of nuclear weapons would always and inevitably lead to a situation where there would be no survivors?

There is limited experience with the use of nuclear weapons in hostilities. But even in Hiroshima and Nagasaki there were survivors. Depending on the size of the nuclear warhead and the location attacked, it would not be an inevitable result that all adversaries would be killed. Also, the ICRC commentary to this provision notes that this rule cannot be seen as prohibiting specific weapons.

The other provision in AP I that explicitly deals with threats, Article 51 (2), states that:

‘Acts or threats of violence the primary purpose of which is to spread terror among the civilian population are prohibited.’

According to the ICRC commentary, the second sentence of Article 51(2) applies to acts or threats of terror that go beyond ordinary acts of war. Ordinary acts of war in most circumstances are terrifying to those who might be at the receiving end or in the vicinity of such acts, but this provision is intended to prohibit threats of violence, the primary purpose of which is to spread terror among the civilian population without offering substantial military advantage.

A threat to use nuclear weapons could of course be made in violation of this rule. It would depend on the circumstances and on the intent behind the threat. But this is not the same as saying that all cases of threats to use nuclear weapons would violate this provision. The criterion of the primary purpose of the threat must be fulfilled. Article 51(2) cannot therefore constitute a general ban on a specific weapon.

One of the main purposes of IHL is to regulate the conduct of hostilities. Throughout IHL’s history, the actual conduct of hostilities has been the concern of IHL, not threats. There is no general prohibition on threats to violate IHL. Hence, none of the treaties prohibiting categories of weapons contain prohibitions on threats.

The blurring of the lines between threats and use in an IHL context reinforces the blurring of the lines between the rules pertaining to the war’s justification and the rules regulating conduct of hostilities. The threat of use of force, prohibited under the UN Charter, has somehow landed in the IHL debate without sufficient legal justification.

And if these two legal regimes cannot be kept separate, if IHL is not seen as a regime that applies in war and thus also in extreme situations of self defence, then IHL may be seriously undermined.

* The side event at which this presentation was held was hosted by the government of New Zealand.

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